There are four valves in the heart. These valves are designed to control the flow of blood through the heart to ensure that the blood flows in only one direction. Valves can fail in one of two ways: either they don't open properly, in which case they become stuck (stenotic), or they don't close properly, in which case they become leaky (regurgitant). One valve in particular, the mitral valve, is prone to leaks. A leak in the mitral valve results in a disorder known as mitral regurgitation. Mitral regurgitation occurs when the leaflets of the heart's mitral valve (anterior and posterior) do not close properly thus causing a leak.
During the heart's contraction, a leak in the mitral valve results in a reversal of blood flow. Blood ‘backs up’ into the left atrium, thereby decreasing blood flow to the body and increasing congestion of the lungs. Although the heart can usually compensate for this leak in the short term, in the long term, the heart loses its ability to compensate, thus leading to gradual or sudden decompensation. Such decompensation includes enlargement of the heart chamber and weakening of the heart muscle. Flooding of the lungs leads to pulmonary edema and pulmonary hypertension, both of which can lead to permanent damage to the lung tissue. Such changes, if detected and corrected early, may be reversible. If left unchecked, such changes will lead to heart failure and death. As such, a severely leaking mitral valve is almost always an indication for surgical repair.
Until recently, the only method for repairing the mitral valve required open heart surgery. Although such an approach has proven benefits, it comes with a certain degree of risk due to the invasiveness of the operation. As such, the risks involved in the operation are often deemed to be too high for some patients, whom, unfortunately, have to be refused treatment. These patients generally go on to die from their disease.
Recently, a new technology was introduced whereby the mitral valve can be repaired through a catheter without the need for surgery. The procedure, known as the MitraClip™ procedure is based on the “Alfieri” method of mitral valve repair whereby a suture is placed surgically to join together the two (anterior and posterior) leaflets of the mitral valve, thus promoting proper closure. As a minimally invasive, non-surgical alternative, the MitraClip™ procedure enables clipping together of the two leaflets, thus creating a bridge, resulting in a double orifice opening. The bridge may include the clip or suture, which eventually heals over with endothelial tissue. The mitral valve continues to open on both sides of the bridge when the heart relaxes, and closes as required when the heart contracts.
The Alfieri and MitraClip® procedures involve, for example, inserting a catheter through a vein in the groin. The catheter is guided up to the mitral valve under x-ray and ultrasound guidance. Once above the valve, the catheter deploys a clip which joins the anterior and posterior leaflets at the midpoint of the valvular opening. The clip effectively reduces the leak, sometimes eliminating it entirely. The procedure is extremely gentle, and very low risk, even in the most elderly and ill patients. This is currently the only device of its kind on the market.
It is expected that the MitraClip™ will remain a first line therapy for treating mitral regurgitation in selected patients for a number of years. However, new technologies are currently under development which would allow the mitral valve to be replaced entirely through a catheter (Transcatheter Mitral Valve Replacement). Although these technologies are still some time away from clinical application, they may provide an alternative to the Alfieri and MitraClip™ procedures in select patients. Furthermore, in cases where the Alfieri or MitraClip™ procedure fails, it is expected that the best option will be mitral valve replacement. Unfortunately, the mitral valve cannot be replaced using transcatheter methods in the presence of a tissue bridge, suture or clip. There is therefore a need for a minimally invasive, catheter based approach to safely remove a tissue bridge, a MitraClip™, a suture, or any other clip device.
There are currently numerous medical devices in use for the removal of tissue from body cavities. However, these devices are not appropriate for use in removing tissue from the heart. Instrumentation for use in heart procedures is very different than instrumentation that may be used in other parts of the body. Firstly, the heart is blood filled, such that no direct visualization can be used, as would be the case with endoscopic devices. Secondly, the heart is mobile and continuously beating, making instrumentation more difficult and potentially hazardous. For these reasons, most cardiac instrumentation involves the use of guidewire technology. This is essential to minimize the risk of cardiac or vascular injury/perforation during manipulation. In contrast, most tissue biopsy devices do not require as exact positioning as do intracardiac devices. Finally, when instrumenting the mitral valve, there is a risk of entanglement of any device with the sub-valvular apparatus which is comprised of a series of cord-like structures which support the valve leaflets, much like a parachute. With guidewire technology, this possibility is mitigated. The ability to steer an apparatus using guidewire technology in the area of the heart valves enables accurate positioning and guidance that is necessary to navigate a clip or suture removing apparatus through two orifices of a double orifice valve.
U.S. Patent Application Publication No. 20080009858A1 discloses a device which is designed to clamp, cauterize, excise and retrieve tissue from the abdomen. This device is not designed to be delivered or applied intravascularly. Moreover, the device could not be utilized intravascularly as electrocautery is ineffective in the presence of a fluid interface. Instead, the device is designed solely for endoscopic use within the abdomen, chest or pelvis. The need for electrocautery as an excision tool is for the purpose of ensuring hemostasis (absence of bleeding following excision). This is not an issue within the heart. Further, the device is not designed to be compatible with guidewire technology.
U.S. Patent Application No. 20060184198A1 discloses a device which is a biopsy forcep designed for use endoscopically. The device consists of jaws which grasp a tissue and a knife which cuts tissue within the jaw. The device is not designed to be used intravascularly and cannot be used with guidewire technology. In addition, the device would not be safe for use within the heart, as the piercing blade is not retractable. In the case of the mitral valve, the blade would be exposed to heart tissues when the jaws are open, thus increasing the risk of injury to normal structures. The cutting mechanism enables for a linear incision within a single plane rather than a circumferential incision, which would be necessary for excision of a mitral tissue bridge.
In some aspects, it may be desirable to provide an apparatus that effectively and safely removes a clip or a suture from the mitral valve to enable placement of a new mitral valve. The device must also be able to safely retrieve the excised clip, suture and/or tissue bridge to prevent intravascular embolization. In some aspects, it may be desirable to provide an apparatus that effectively and safely cuts part of at least one leaflet of the mitral valve to remove the bridge that has been created by the clip or suture. There is a need for such devices that may be deployed through a catheter and which can be used safely and effectively in the heart in proximity to a functioning heart valve.